| ( | x | ( | 7 5 | + | x | ) | ( | x | − | 1 10 | ) | ) | ÷ | 2 | = | 13 20 |
| 方程左边 = | x | ( | 7 5 | + | x | ) | ( | x | − | 1 10 | ) | × | 1 2 |
| = | x | × | 7 5 | ( | x | − | 1 10 | ) | × | 1 2 | + | x | x | ( | x | − | 1 10 | ) | × | 1 2 |
| = | x | × | 7 10 | ( | x | − | 1 10 | ) | + | x | x | ( | x | − | 1 10 | ) | × | 1 2 |
| = | x | × | 7 10 | x | − | x | × | 7 10 | × | 1 10 | + | x | x | ( | x | − | 1 10 | ) | × | 1 2 |
| = | x | × | 7 10 | x | − | x | × | 7 100 | + | x | x | ( | x | − | 1 10 | ) | × | 1 2 |
| = | x | × | 7 10 | x | − | 7 100 | x | + | x | x | x | × | 1 2 | − | x | x | × | 1 10 |
| = | x | × | 7 10 | x | − | 7 100 | x | + | x | x | x | × | 1 2 | − | x | x | × | 1 20 |
| x | × | 7 10 | x | − | 7 100 | x | + | x | x | x | × | 1 2 | − | x | x | × | 1 20 | = | 13 20 |